The present application claims priority to Japanese Application No. P2000-081578 filed Mar. 23, 2000, which application is incorporated herein by reference to the extent permitted by law.
The present invention relates to a lithium ion battery such as a lithium ion polymer secondary battery having a gel-type or plastic macromolecular electrolyte layer, and a method of manufacturing the same.
In recent years, accompanying by a situation that portable small electric equipment such as small, lightweight cellular phones or portable computers has been popularized, second batteries having small, reliable output characteristics and capable of longtime use by recharging many times such as nickel-cadmium batteries, nickel-hydrogen batteries and lithium ion batteries has been studied and developed vastly as an electric source for supplying electric power to drive the electric equipment.
Among the secondary batteries, the lithium ion secondary battery has characteristics capable of outputting stable electric power despite its small, lightweight, thin in size, and has studied and developed for the purpose of employing as a foldable secondary battery by taking advantage of suitable structural characteristics for its thin size.
Further, as technique capable of achieving the above-mentioned thin size and foldable shape, and of gaining superior characteristics free of leakage unlike the case of employing liquid electrolyte as a dry cell, it is suggested that a technique employs gel-type electrolyte including plasticizer realizing flexibility, and a technique employs macromolecular solid electrolyte, in which a lithium salt is dissolved in a macromolecular material.
In such lithium ion secondary batteries with a thin structure, generally, the main part of the battery is formed in the following manner. A laminating structure is formed by laminating a positive electrode, a positive electrode active material layer, a gel-type macromolecular solid electrolyte layer, a separator, a negative electrode, a negative electrode active material layer. A positive electrode lead and a negative lead electrode joints to the corresponding electrodes in the laminating structure. After this, the laminating structure is covered with package members made of aluminum/polypropylenexe2x80xa2laminate pack material, and sealed ends.
As for materials used for the above-mentioned schematic structure, for instance, materials described later can be preferably used. Plastic materials employed here are shortened hereinafter: polyethylene terephthalate; PET, fused polypropylene; PP, cast polypropylene; CPP, polyethylene; PE, low-density polyethylene; LDPE, high-density polyethylene; HDPE, linear low-density polyethylene; LLDPE, nyron; Ny. Additionally, aluminum, which is a metal material employed as a barrier film having moisture permeability resistance, is shorten as AL.
The most typical structure is a combination such that a package member, a metal film and a sealant layer are respectively PET, AL, and PE. Other typical laminating structures can be also employed as the same as this combination. Such combinations are: PET/AL/CPP, PET/AL/PET/CPP, PET/Ny/AL/CPP, PET/Ny/AL/Ny/CPP, PET/Ny/AL/Ny/PE, Ny/PE/AL/LLDPE, PET/PE/AL/PET/LDPE, or PET/Ny/AL/LDPE/CPP.
As for materials employed as the sealant layer of a laminating film, the above-exemplified PE, LDPE, HDPE, LLDPE, PP, and CPP and the like can be employed, and its thickness is preferably in a range of 20 xcexcmxcx9c100 xcexcm based on the observed results. The fusion temperature of the materials employed as the sealant layer are generally hereinafter. The fusion temperature of PE, LDPE, HDPE and LLDPE are within a range of 120-150xc2x0 C., that of PP and CPP are about 180xc2x0 C., and the fusion temperature of PET employed as the package layer is over 230xc2x0 C.
As materials employed as a barrier film having moisture permeability resistance, although aluminum is exemplified in the above example, it is not limited, and materials capable of forming thin films by means of sputtering can be employed. As for such materials, alumina (Al2O3), silicon oxide (SiO2), and silicon nitride (SiNx) can be employed.
In a conventional means for sealing the ends of the package members of the lithium ion secondary battery with a thin structure, generally, adhesive material with high adhesion for the metal material and the package members of the lead electrodes, is applied on a position where the ends of the package members are sealed, and pressure is applied on the position to be sealed. In another means, the adhesive material is only applied to surfaces of the sealed positions in each of the lead electrodes and the ends of the package members are applied pressure to each of the lead electrodes so as to seal the part.
However, in the conventional sealing structure and method of manufacturing the same using the adhesive material as described above, there are problems such that even if the package members can be completely sealed to principal surfaces of the lead electrodes, gaps are easy to be produced between sides of the lead electrodes and the package members, which causes an incomplete sealing state (or hermeticity decrease), thereby, insides of the batteries are susceptible to influence of temperature variations or influence from the outside, and by secular change in the batteries, the insides of the batteries deteriorates rapidly, which results in decrease of electromotive force and reduction of durability. Additionally, such batteries occurred the gaps causing degradation of battery capability, must be treated as a nonconforming battery, which results in productivity decrease.
The invention has been achieved in consideration of the above problems and its object is to provide a lithium ion battery with high productivity and excellent in hermeticity inside the battery covered with a package member by means of preventing sealing failures caused by a gap occurred between sides of a lead electrode and the package member, and a method of manufacturing the same.
A nonaqueous-electrolyte secondary battery according to the present invention comprises a laminating structure, in which at least a positive electrode and a negative electrode are laminated, a film-like or sheet-like package member for covering the laminating structure, a lead electrode whose one end joints to the laminating structure and the other end protrudes toward the outside from an end of the package member, and a sealing member, which is inserted between the end of the package member and the lead electrode by fusing a thermoplastic material, and seals the gap therebetween.
In a method of manufacturing a nonaqueous-electrolyte secondary battery according to the present invention, a step of sealing a gap between a lead electrode and an end of a package member, whereby a sealing member made of a thermoplastic material is inserted between the lead electrode and the end of the package member, wherein the electrode whose one end connects to the laminating structure and the other end protrudes from the end of the package member toward the outside, and the sealing member fuses in order to seal the gap therebetween.
Further, a method of manufacturing another nonaqueous-electrolyte secondary battery according to the present invention comprises a step of sealing a gap between a lead electrode and an end of a package member, whereby a sealing member made of a thermoplastic material is inserted between a lead electrode and the end of the package member, wherein the electrode whose one end joints to a laminating structure and the other end protrudes from an end of a package member toward the outside, a heater is applied to heat to the ends of the sealing member for fusion at temperature over its fusion temperature from the outer side.
Further more, a method of manufacturing another nonaqueous-electrolyte secondary battery according to the present invention comprises a step of sealing a gap between a lead electrode and an end of a package member, whereby the sealing member made of a thermoplastic material is inserted between the end of the package member and the lead electrode whose one end joints to the laminating structure and the other end protrudes from the end of the package member toward the outside, a heater is applied pressure to at least the end of the package member from the outside, a stripping sheet made of a material such that at least its surface does not adhere to the sealing member, is inserted, then the heater is generated heating to the sealing member at temperature over its fusion temperature for fusion.
A method of manufacturing another nonaqueous-electrolyte secondary battery according to the present invention comprises steps of fusing a sealing member, whereby the sealing member is inserted between a lead electrode whose one end joints to the laminating structure, and the other end protrudes from an end of the package member, at least pressure is applied to the end of the package member from the outside, a stripping sheet made of a material such that at least its surface does not adhere to a sealing member, is inserted between a heater and the package member, or the sealing member, and of separating the stripping sheet from the package member, or the sealing member whereby after the sealing member can spread between the lead electrode and the package member without a gap after heating and fusing the sealing member, the stripping sheet is separated from the heater, then the fused sealing member re-solidifies to be made in a solid state.
A method of manufacturing another nonaqueous-electrolyte battery according to the present invention comprises steps of fusing a sealing member, whereby the sealing member made of a thermoplastic material is disposed in a predetermined position of a lead electrode, pressure is applied to at least the sealing member from the outside, a stripping sheet made of a material such that at least its surface does not adhere to the sealing member, is inserted between the heater and the sealing member, and of separating the stripping sheet from the package member, whereby after sealing member can spread between the lead electrode and the package member without a gap by heating and fusing the sealing member, the stripping sheet is separated from the heater, then after the fused sealing member re-solidifies to be made in a solid state.
In a nonaqueous-electrolyte secondary battery and a method of manufacturing the same, since a sealing member made of a thermoplastic material is fused and inserted between an end of a package member and a lead electrode for sealing a gap, the sealing member can spread therebetween. Since the sealing member adhere to the lead electrode by fusing the sealing member, the sealing member adhere to the lead electrode without a gap.
In a method of manufacturing a nonaqueous-electrolyte secondary battery according to the present invention, during a step of sealing a gap between an end of a package member and a lead electrode by fusing and inserting a sealing member, since a stripping sheet made of a material such that at least its surface does not adhere to the sealing member, is inserted into the package member or the sealing member and the heater, the heater is applied pressure and generated heating to the package member or the sealing member, even if the fused sealing member is leaked or forced out from the end of the package member toward the outside, it does not adhere to a surface of the heater.
Additionally, since the stripping sheet has a sheet-like shape unlike the case it is annexed to the surface of the heater in a flat shape, the heater presses the stripping sheet in a manner of shaping along with a concave-convex shape of the sealing member, thereby, even if after the sealing member fuses and spreads between the package member, the package member and the sealing member are soon stripped from the heater with the stripping sheet, the shape of the sealing member and the state of the lead electrode can be maintained until the sealing member re-solidifies to be made in a solid state.
For this reason, without letting the heater is repeated to heat and cool itself, when heating generated is necessary, the heater pressed the package member and the sealing member in order to fuse the sealing member, then on the sealing member fuses enough, the heater is separated from the package member covered with the stripping sheet and the sealing member, which gives the time when the sealing member cools and re-solidifies at room temperature, or by forced cooling wind. This also maintains the shape of the sealing member even if the heater is apart when the sealing member does not solidify yet. From this point, the stripping sheet is desirable used in a sheet-like state, which can be separated from the heater rather than coating on the surface of the heater.
In the case that the above-mentioned lithium ion battery is a solid electrolyte battery, or gel-type electrolyte gel, as a macromolecule material employed for macromolecular solid electrolyte, silicon gel, acryl gel, acrylonitrite gel, polyphosphazen denatured polymer, polyethylene oxide, polypropylene oxide, and composite polymer of the above-mentioned materials, cross-linked polymer of the above-mentioned materials, denatured polymer of the above-mentioned materials can be employed, as for fluorine polymer, for example, poly(vinylidenefluororide), poly(vinylidenefluororide-co-hexafluoropylene), poly(vinylidenefluororide-co-tetrafluoroethylene), poly(vinylidenefluororide-co-trifluoroethylene) and mixture of the above-mentioned materials can be employed. Additionally, various materials can be also employed as the same as the above-mentioned materials.
As for solid electrolyte, or gel-type electrolyte stacked on a positive electrode active layer, or a negative electrode active layer, preferable materials are made by the following processes. First, a solution comprising a macromolecular compound, an electrolyte salt, and a solvent, is impregnated into the positive electrode active material, or the negative electrode active material in order to remove the solvent, and solidifies. The solid electrolyte, or the gel-type electrolyte stacked on the positive electrode active layer, or the negative electrode active layer is impregnated into the positive electrode active layer or the negative electrode active layer, and solidifies. In case of a cross-linked material, after the above-mentioned processes, light or heat is applied to conduct cross-liking to solidify.
The gel-type electrolyte is made of plasticizer including a lithium salt and a matrix macromolecule in the range of equal to or more than 2 percentage by weight and equal to or less than 3 percentage by weight. At this moment, esters, ethers, and carbonic acid esters can be employed independently, or as one component of plasticizer.
When adjusting the gel-typed electrolyte, as for the matrix macromolecule gelling the above-mentioned carbonic acid esters, although various macromolecules employed for forming the gel-type electrolyte, fluorine macromolecules such as poly(vinylidenefluororide), poly(vinylidenefluororide-co-hexafluoropropylene) are preferably employed from reduction-oxidation stability point of view.
The macromolecular electrolyte is made of the lithium salt and the macromolecular compound, in which the lithium salt is dissolved. As for the macromolecular electrolyte, ether macromolecule such as poly(ethylene oxide) and cross-linked polyethylene oxide, poly(methercrylateester), acrylates, fluorine macromolecules such as poly(vinylidenefuluororide), poly(vinylidenefluororide-co-hexafluoropropylene) can be employed independently, or as a mixture among the above-mentioned materials. From reduction-oxidation stability point of view, preferably, the fluorine macromolecules such as poly(vinylidenefluororide) or poly(vinylidenefluororide-co-hexafluoropropylene) can be employed.
As the lithium salt included in the gel-type electrolyte or the macromolecular solid electrolyte, a lithium salt used for typical electrolyte as a battery can be employed. More detail, the following materials are considered: lithium chloride; lithium bromide; lithium iodide; chloric lithium; lithium perchlorate; lithium bromate; lithium iodate; lithium nitrate; tetrafluorolithiumborate; hexafluorophosphoriclithium; lithium acetate; bis(trifluoromethanesulfonil)imidelithium, LiAsF6, LiCF3SO3, LiC(SO2CF3)3, LiAlCl4, LiSiF6. In case of the gel-type electrolyte, preferable dissolution density of the lithium salt is in the range of 0.1 to 3.0 mol in plasticizer, more preferably, in the range of 0.5 to 2.0 mol. Additionally, the kinds of the lithium salt, or its dissolution density is not limited by the above-mentioned materials and dissolution density.
As a negative electrode material, a material capable of doping or un-doping lithium is preferable. As such a material, for example, a non-graphitizing carbon material, or a graphite material is preferably employed. Further detail, pyrocarbons, cokes (pitch coke, needle coke, petroleum coke), graphites, glassy carbons, organic macromolecular compound calcinated materials (materials such that phenolic resin, furan resin and the like are calcinated at proper temperature), carbon fiber, carbonaceous materials such as activated carbon can employed. As for other materials, macromolecules such as polyacetylene, polypyrrole or oxide such as SnO2 can be employed. In a case of forming a negative electrode using such materials, well-known binders may be doped.
On the other hand, a positive electrode can be formed using metal oxide, metal sulfide or specific macromolecules as positive electrode active materials, depending on kinds of achieved batteries. Take the case where lithium ion batteries are formed, for instance, as the positive electrode active material, metal sulfide or metal oxide such as TiS2, MoS2, NbSe2, V2O5 which includes no lithium, or lithium complex oxide mainly including LiMO2 and the like can be employed. As for transition metal M forming lithium complex oxide, Co, Ni, Mn are preferable. LiCoO2, LiNiO2, LiNiyCol-yO2 and the like can be considered as specific examples of such lithium complex oxide. In the formula described before, M represents equal to or more than one kind of transition metal, x is a value satisfying in accord with a discharge state of the battery, typically in the range of 0.05 to 1.10, y is a value satisfying by formula: 0 less than y less than 1. These lithium complex oxide are capable of generating high voltage, which forms the positive electrode active material having excellent characteristics in energy density. A plurality of the positive electrode active materials may be used for the positive electrode by mixing. When forming a positive electrode using the positive electrode active material, well-known conducting agents or binders can be doped.
Other and further objects, features and advantages of the invention will appear more fully from the following description.